1. Field of the Invention
The present invention relates to a focal point detection device for detecting a focus state of an imaging lens. Furthermore, the present invention also relates to a camera system furnished with the focal point detection device.
Priority is claimed on Japanese Patent Application No. 2008-248749, filed Sep. 26, 2008, the content of which is incorporated herein by reference.
2. Description of Related Art
Cameras that perform auto-focus (referred to hereunder as AF) processing, in which the focus state of an imaging lens is detected and corrected automatically such that it becomes focused, have become mainstream (for example, refer to Japanese Unexamined
Patent Application, First Publication No. 2001-255450). In AF processing, firstly, processing using a high pass filter (referred to hereunder as HPF) is performed on an image signal output from an imaging device. Subsequently, integrated processing is performed on each of a plurality of regions obtained by dividing a single- field image, and an AF evaluation value is calculated for each region. In the case where the imaging lens is not focused, since the obtained image is blurred, the AF evaluation values are low. Furthermore, in the case where the imaging lens is focused, since edges appear in the obtained image, the AF evaluation values are high. Based on the AF evaluation values obtained as described above, the location of the imaging lens is controlled by hill climbing control system or the like, for example, such that the AF evaluation value in a desired region reaches a maximum.
Normally, an IIR (Infinite Impulse Response) filter is used for the HPF. This is because it contains a feedback group, and hence excellent characteristics can be obtained in low order compared with a FIR (Finite Impulse Response) filter. In the case where the HPF is formed using an IIR filter, a multiplier or an adder incorporated in the feedback loop of the IIR filter has to process an image signal within one clock cycle.